The UFO Phenomenon

4.2 light years = 39.73E+15 metres, so r^2 would be 1.6E+33 ... and that's a mahoosive number.

 

 

 

/edit: Intensity(Physics)

 

I've just calculated¹ the transmitter power needed to send a signal to our nearest stellar neighbour (Proxima Centauri ) 4.2 light-years away that will arrive there with the same energy density as the Cosmic Microwave Background radiation... and it's 240 zettawatts (240,000,000,000,000,000,000KW).

 

 

...and our Sun is only 1,680 times more powerful than that.

 

So based upon that we are essentially invisible to any alien civilisation no matter where they are.

 

 

 

¹ I have to admit the number surprises even me, I may have made a silly error, so anyone who can confirm or deny my calculations is welcome to have a go.

You would think that given all the sources of radio transmission we have (radio, TV, radar, cell-phones, wifi, bluetooth, garage door openers, microwave ovens, remote control, remote monitoring, emergency bands, GPS, ship to shore, air traffic control, walkie-talkies, cb-radio, ham radio, military comms, etc) that our technology fingerprint would be huge and would be broadcasting our presence into space like a huge flashing beacon announcing "HERE WE ARE" with such emphatic disregard for the peace and quiet of our interstellar neighbours it is little wonder we've not had a visit from the intergalactic police requesting us (very politely of course) to turn the bloody noise down.

 

The problems of detecting our technological finger-print from the vast distances of space is more than just a problem of distance. As has already been commented, the electromagnetic radiation we produce are very weak. Just how weak these are cannot be overstated - we know that we are producing a lot of EM radiation here on Earth, we just have to buy a radio receiver to detect it. When you consider that each of the 44,000 FM radio station in the world broadcasts with a typical power of 100kW (giving a total of 4.4 billion watts), each of the 6 billion cell phones that exist in the world are transmitting with a typical power of ½W each (giving a total of 3 billion watts) then the gross amount of EM radiation we are producing when you factor in the really powerful stuff like communication satellite up-links and general satellite broadcasts such as TV and GPS and the cell-phone networks, it easily runs to numbers that can be measured in terawatts. Surely this is easy to detect from space?

 

The problem for the extraterrestrial listener is that much of this EM radiation does not leave the local confines of the Earth. How much is determined by the kinds of antenna used by the various transmitters we have and how powerful those transmitters are.

 

An ideal point-source transmitter radiates radio waves equally in all directions (x, y and z) and are called "isotropic" and are barely more than theoretical - the closest we have to the theoretical isotropic radiator are the spark-gap transmitters of the 19th century experiments into radio broadcasting - and they are an extremely inefficient use of power when what you are trying to do is communicate between two points on the surface of the Earth, plus any signals transmitted up into the sky (the z-axis) are a waste of power. These transmitters are not only inefficient, they are also very low powered, permitting communication of a few hundred metres at best. Even though these antenna are isotropic and therefore radiate upwards, the radio waves produced would not be powerful enough to be detected from beyond our atmosphere.

 

The next kind of antenna is a dipole, this aerial only transmits in the x and y axis in a doughnut shape giving a more efficient use of transmitter power - most radio uses this method (broadcast AM & FM radio, non-satellite TV, cell-phones, home wifi hubs, bluetooth devices, military and aircraft comms etc) - we call these "omnidirectional" but in reality they only transmit horizontally (x and y) and not into space.

 

The third kind of antenna has reflectors and directors to focus the beam of radio waves into a cone shape (often cardioid due to the inefficiencies of the reflectors), these are sometimes called "beam" or "directional" and only transmit in the x-axis. Variants on these are parabolic dishes and the like that we use in radar and to communicate with satellites. When it comes to satellite communications the only source we need consider is up-link, since any down-link (TV and GPS) is obviously pointing to the Earth and not out into space.

 

Next thing to consider is transmitter power itself - a ½W cell-phone is not going to reach more than 30km at best (and those of us who live in rural areas find even that to be optimistic), most FM radio stations have a range of less than 100 miles - and since the antenna used in both those transmitters does not radiate upwards we can discount them as a source for our alien to detect, along with wi-fi, bluetooth, microwave ovens, aircraft comms, emergency band and many other low power terrestrial point-to-point radio communication routes.

 

Since radio waves travel in straight lines one would assume that the Earth-based omnidirectional and directional antenna would beam their signals towards the horizon and keep going through the atmosphere and out into space allowing our distant alien to eventually detect them. Unfortunately it's not as simple as that.

 

One of the layers of the atmosphere of interest to radio specialists is the Heaviside layer, this is a layer of ionised gases some 90-150 km above the surface of the Earth - lower to medium frequency radio waves have a tendency to bounce off this layer back down to Earth, this is why we can receive radio transmissions from beyond the horizon, and it is also why little of these transmissions will leave the Earth and radiate into space.

 

Another problem with radio waves is they are easily attenuated by anything that gets in their way - we all know that anything conductive can shield radio waves, this goes for anything with a high water content such as clouds, and we know that for higher frequencies any solid object can block the wave (X-Rays) and others objects can bounce or reflect them (radar).

 

Atmospheric events can also disrupt radio transmission, solar flares, aurora, electrical storms, rain... all affecting how any stray signals can leak out into space. Another barrier has to contend with for any signals that manage to escape the Earth's atmosphere is the Van Allen radiation belt, which can also attenuate or generally affect the signals, and as I said in a previous post, we really don't know what effect the Oort cloud will have on these EM waves.

 

Therefore while we are indeed creating terawatts of EM radiation here on Earth, not very much of that gets out into space and what little that does has to contend with the inverse-square law when traversing the large distances between stars. As Pat and I have said, our radio signals are very weak and space is very big.

 

So, what if our alien civilisation is very advanced had has some really sensitive receivers? In the old days of terrestrial broadcast television I could easily demonstrate the next problem the alien has to negotiate, and that is static. De-tune an analogue TV set and you can see and hear the static being received - a lot of that static is thermal noise and about one-third of it is the Cosmic Microwave Background Radiation of the big-bang, once the signal you are looking for disappears below that it is lost. As we know from Earth-based radio and TV reception, the only way to improve reception (and therefore range) is to increase transmitter power, not receiver sensitivity.

Oh the irony